Re: everyone's messages

Samuel Rivier wrote:

> All planets that spin have magnetic fields.
No.  The mechanisms that create planetary magnetic fields are rather
complex.  You can read about them under
http://www.ucl.ac.uk/geolsci/edu/students/planet/student/work/magrev/magtoc.htm.

For example, Venus and Mars don't have an intrinsic field of their own.
Interactions with the solar wind do induce a weak magnetic field in the
ionosphere, but couldn't use a magnetic compass on their surface.

Anyway, it seems arbitrary and pointless to define North after a
phenomenon that can be infinitesimally weak, unstable through time, and
inconsistent with geographic coordinates, if one could simply use the
unambiguous and universally applicable definition of the angular momentum.


-- Christian Thalmann